KR100601613B1 - Phase change optical medium - Google Patents

Abstract

A layer structure in which a first dielectric layer, an interference layer, a second dielectric layer, a recording layer, a third dielectric layer, and a reflection layer are sequentially stacked on a substrate or an interference layer, a first dielectric layer, a second dielectric layer, a recording layer, and a third dielectric layer on a substrate. And the formation of a layer structure in which the reflective layers are sequentially stacked to increase the light absorption ratio (Ac / Aa) between the crystalline and amorphous phases of the recording layer, so that the jitter value at the time of overwriting can be reduced even when the blue wavelength light is used as the light source. Disclosed is a phase change optical disc capable of reducing and at the same time suppressing the occurrence of cross-erase.

Description

Phase change optical medium

1 is a vertical cross-sectional structural view schematically showing an example of a conventional phase change optical disk,

Figure 2 is a vertical cross-sectional structure schematically showing another example of a conventional phase change optical disk,

3 is a graph schematically showing optical characteristics according to a thickness of a first dielectric layer of a conventional phase change optical disk shown in FIG. 1;

4 is a graph schematically showing optical characteristics according to a thickness of a first dielectric layer of a conventional phase change optical disk shown in FIG.

5 is a vertical cross-sectional structural view schematically showing an example of a phase change optical disk according to the first embodiment of the present invention;

FIG. 6 is a graph schematically showing optical characteristics according to the thickness of the first dielectric layer of the phase change optical disk of the present invention shown in FIG. 5;

7 is a schematic vertical cross-sectional structural view showing another example of a phase change optical disk according to the second embodiment of the present invention;

FIG. 8 is a graph schematically showing optical characteristics according to the thickness of the first dielectric layer of the phase change optical disk of the present invention shown in FIG.

9 is a graph schematically showing a typical recording laser pulse of a phase change optical disk;

10 is a cross-sectional view schematically showing a track structure of a phase change optical disk;

11 is a graph schematically showing a temperature distribution according to each distance from a track center of a conventional phase change optical disc and a phase change optical disc according to the present invention.

<Description of Symbols for Major Parts of Drawings>

110 substrate 120 first dielectric layer

130 ... interference layer 140 ... second dielectric layer

150 ... recording layer 160 ... third dielectric layer

170 ... reflective layer 210 ... substrate

220 Interference layer 230 First dielectric layer

240 second dielectric layer 250 recording layer

260 ... third dielectric layer 270 ... reflective layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change optical disk in which optical characteristics of a recording layer are changed by irradiation of a laser beam. In particular, when a blue laser beam is used as a light source, jitter value reduction and cross-erasing (overwriting) are performed. A phase change optical disk having a layer structure capable of suppressing cross-erase) generation.

A phase change optical disk is an optical information recording medium for recording, reproducing, and erasing information by irradiation of a laser beam. The phase change optical disk has a relatively easy configuration of an optical head and a so-called overwriting that simultaneously records and erases. Due to such features, researches for increasing the density have been actively conducted.

The phase change optical disk records and reproduces information using a property in which the recording layer of the portion to which the laser beam is irradiated becomes crystalline or amorphous according to the power and cooling speed of the incident laser beam, thereby changing its optical characteristics. do. That is, in the case of recording, it is possible to melt the recording layer initialized to a crystalline phase by irradiation of a laser beam by short pulses to high powder recording pulses, and then amorphous by quenching to generate recording marks. In the reproduction of information on the recording mark, since the light reflectance in the crystalline and amorphous states is different when the laser beam incident on the optical disk is reflected from the recording layer, the difference in reflectance is detected by the photodetector and reproduced as an electrical signal. do. In the case of erasing a recording mark, the recording mark is erased by crystallizing the recording mark of the amorphous layer by an erase pulse of low powder at long pulses.

Such a phase change optical disk has a lower light absorption rate Aa in the amorphous recording layer in order to suppress so-called cross-erase generation, which is a phenomenon in which marks of adjacent tracks are partially erased during recording. That is, the larger the ratio (Ac / Aa) of the light absorption rate Ac in the crystalline state of the recording layer to the light absorption rate Aa in the amorphous state, the better.

In addition, in order to not change the size of the recording mark during overwriting in which recording pulses are superimposed on the erase pulses to simultaneously perform recording and erasing, the light absorption ratio (Ac / Aa) in the crystalline and amorphous states of the recording layer is 1.1 to It is well known that it should have a value of about 1.2.

Therefore, the high density phase change optical disk must satisfy the essential condition that the light absorption ratio (Ac / Aa) in the crystalline and amorphous state of the recording layer should have a value of 1.2 or more.

In a phase change optical disc using a conventional red or near-infrared laser beam as a light source, the optical absorption ratio (Ac / Aa) in the crystalline and amorphous states of the recording layer is shown in FIGS. 1 and 2 so as to have a value of 1.2 or more. It is formed into a multilayer structure as shown.

The conventional phase change optical disk 10 shown in FIG. 1 includes, for example, an Au interference layer 12 and a first dielectric layer 13 on a substrate 11 formed of a transparent acrylic resin material, a polycarbonate (PC) material, or the like. When the laser beam is irradiated, the recording layer 14, the second dielectric layer 15, and the reflective layer 16, which are formed of a phase change material whose state changes, are sequentially stacked.

Usually, a GeSbTe-based material such as ZnS-SiO ₂ as the first dielectric layer 13 and the second dielectric layer 15, Ge ₂ Sb ₂ Te ₅ as the recording layer 14, and aluminum (Al) as the reflective layer 16. ) Or an aluminum alloy material is used.

In the conventional phase change optical disk 10, the optical wave reflected from the interference layer 12 and the optical wave reflected from the crystalline recording layer 14 cause a destructive interference, so that when the recording layer 14 is crystalline, Since the reflectance is greatly reduced, the light absorption rate is increased. On the other hand, when the recording layer 14 is amorphous, since it has a high reflectance, the light absorption in the amorphous recording layer 14 is reduced.

Therefore, the conventional phase change optical disk 10 shown in FIG. 1 has a light absorption ratio (Ac / Aa) in a crystalline and amorphous state of the recording layer 14 when using a red or near infrared laser beam as a light source. It is possible to have a value of 1.2 or more.

However, when the conventional phase change optical disk 10 shown in FIG. 1 uses blue wavelength light, that is, a 400 nm laser beam, as a light source, the Au interference layer 12 has a light reflectance in near infrared or red wavelength light. While it is 90% or more, it decreases to 40% in blue wavelength light, making it difficult to cancel interference the light waves reflected from the crystalline recording layer 14.

This is because when the blue wavelength light, i.e., a 400 nm laser beam, is used as the light source, in the phase change optical disk structure of FIG. 1, the light reflectance difference in the crystalline and amorphous state of the recording layer 14 according to the thickness of the first dielectric layer 13 ( Rc-Ra), the light absorption ratio (Ac / Aa) and the phase difference can be confirmed from FIG.

Therefore, in the case where the phase change optical disk using the blue wavelength light as the light source is formed in the layer structure including the Au interference layer 12 as shown in FIG. 1, as shown in FIG. There is a problem that it is difficult to obtain a value of the light absorption ratio (Ac / Aa) in the amorphous state to 1.05 or more.

The conventional phase change optical disk 20 shown in FIG. 2 includes a first dielectric layer 22, a recording layer 23, a second dielectric layer 24, a heat absorption layer 25, and an interference layer on a transparent substrate 21. (26) has a multi-layer structure in which the layers are sequentially stacked.

Si or Au is used as the heat absorption layer 25, and ZnS-SiO ₂ is used as the interference layer 26. The substrate 21, the first dielectric layer 22, the second dielectric layer 24, and the recording layer 23 are used. Is substantially the same material as the phase change optical disk shown in FIG.

In the structure of the conventional phase change optical disk 20 of FIG. 2, the light wave, the heat absorption layer 25, the interference layer 26, and the interference layer (reflected at the interface between the second dielectric layer 24 and the heat absorption layer 25) The light waves reflected at the interface between the layer 26 and the air layer (or protective layer; not shown) cause an extinction interference with respect to the amorphous recording layer 23, thereby reducing the light absorption rate of the amorphous recording layer 23.

Therefore, the conventional phase change optical disk 20 shown in FIG. 2 has a light absorption ratio (Ac / Aa) in the crystalline and amorphous state of the recording layer 23 when using a red or near infrared laser beam as a light source. It is possible to have a value of 1.2 or more.

However, the conventional phase change optical disk 20 shown in FIG. 2 has a tendency to increase the absorption portion of the refractive index of the amorphous recording layer 23 as the light source moves from the near infrared or red wavelength to the blue wavelength region. When the wavelength light, i.e., a 400 nm laser beam, is used as the light source, the light transmittance of the amorphous recording layer 23 decreases, so that the interference layer 26 is positioned next to the recording layer 23 on the basis of the light incident surface. The layered structure makes it difficult to obtain a sufficient interference effect.

This is because when the blue wavelength light, i.e., a 400 nm laser beam, is used as the light source, in the phase change optical disk structure shown in FIG. 2, the difference in light crystallinity in the crystalline and amorphous states of the recording layer 23 depends on the thickness of the first dielectric layer 22. It can be confirmed from FIG. 4 which shows the result of calculating (Rc-Ra), the light absorption ratio (Ac / Aa), and the phase difference.

Therefore, when the phase change optical disk using the blue wavelength light as the light source is formed in the layer structure as shown in FIG. 2, as shown in FIG. 4, the light absorption ratio (Ac) in the crystalline and amorphous state of the recording layer 23 is obtained. / Aa) has a problem that it is difficult to obtain a value of 0.85 or more.

Accordingly, the present invention was created to solve the problems of the conventional phase change optical disk as described above, and at the same time, when using a blue laser beam as a light source, it is possible to reduce the jitter value during overwriting. It is an object of the present invention to provide a phase change optical disk having a layer structure made of suitable materials capable of suppressing the occurrence of cross-erase.

In order to achieve the above object, the phase change optical disk according to the first embodiment of the present invention is formed by sequentially stacking a first dielectric layer, an interference layer, a second dielectric layer, a recording layer, a third dielectric layer, and a reflective layer on a substrate. It features.

In order to achieve the above object, in the phase change optical disk according to the second embodiment of the present invention, an interference layer, a first dielectric layer, a second dielectric layer, a recording layer, a third dielectric layer, and a reflective layer are sequentially stacked on a substrate. Characterized in that made.

In the phase change optical disks of the present invention according to the first and second embodiments, the first dielectric layer is Al ₂ O ₃ , ZnS-SiO ₂ , Si ₃ N ₄ , SiO ₂ , MgF ₂ , NaF ₂ , LiF ₂ , CaF ₂ and AlF ₂ is preferably made of any one material.

And, the interference layer is preferably made of any one material selected from the group consisting of aluminum (Al), silver (Ag) or gallium phosphorus (GaP) and the alloy containing them, the thickness is formed to be 20nm or less. desirable.

The recording layer preferably has a light absorption ratio of 1.0 or more in the crystalline and amorphous state and an optical phase difference of 5 ° or less.

Hereinafter, a phase change optical disk according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 5, the phase change optical disk 100 according to the first embodiment of the present invention includes a first dielectric layer 120, an interference layer 130, and a second dielectric layer 140 on a transparent substrate 110. ), The recording layer 150, the third dielectric layer 160, and the reflective layer 170 are sequentially stacked to have a multilayer film structure.

The first dielectric layer 120 is added to increase the light absorption ratio (Ac / Aa) between the crystalline and amorphous phases of the recording layer 150 and to adjust the reflectivity according to the thickness control. It is used, it is formed of any one material selected from Al ₂ O ₃ , ZnS-SiO ₂ , Si ₃ N ₄ , SiO ₂ , MgF ₂ , NaF ₂ , LiF ₂ , CaF ₂ and AlF ₂ .

In addition, the interference layer 130 is made of a material having a high reflectance in the blue wavelength region, and any one selected from the group consisting of aluminum (Al), silver (Ag), or gallium phosphorus (GaP) and alloys containing them. It is made of material.

The substrate 110, the recording layer 150, and the reflective layer 170 may be formed of a material substantially the same as that used for a conventional phase change optical disk. That is, the recording layer 150 is made of GeSbTe-based material such as Ge ₂ Sb ₂ Te _5, and aluminum (Al) or aluminum alloy material is used as the reflective layer 170.

According to the multi-layered film structure, the light absorption in the crystalline layer is increased by destructive interference between the light waves reflected by the crystalline recording layer 150 and the light waves reflected by the interference layer 130, thereby increasing light absorption between the crystalline and amorphous phases of the recording layer 150. Absorption ratio (Ac / Aa) can be raised.

FIG. 6 shows that the first dielectric layer 120 of the phase change optical disk 100 according to the first embodiment of the present invention shown in FIG. 5 is made of Al ₂ O ₃ , and the interference layer 130 has Al of 8 nm. and formed with a thickness, a second dielectric layer 140 and third dielectric layer 160 is a ZnS-SiO ₂ formed to 55nm and 20nm thickness, and the recording layer 150 is Ge ₂ Sb ₂ Te ₅ to 20nm thickness, respectively, In the case where the aluminum (Al) is formed to have a thickness of 100 nm, the reflective layer 170 has a reflectance Rc in the crystalline state of the recording layer 150 and light in an amorphous state while changing the thickness of the first dielectric layer 120. The result of calculating the reflectance (Ra) and the light absorption ratio (Ac / Aa) is shown as a graph.

6, when the thickness of the first dielectric layer 120 is in the range of 30 nm to 66 nm, the light absorption ratio (Ac / Aa) in the crystalline and amorphous state of the recording layer 150 becomes 1.2 or more. have.

Therefore, when the phase change optical disk using the blue wavelength light as the light source is formed in the layer structure as shown in FIG. 5, the light reflectance Rc of the crystalline layer of the recording layer 150 depends on the thickness of the first dielectric layer 120. The light reflectivity (Ra) and the light absorption ratio (Ac / Aa) in the and amorphous phases can be adjusted to 1.2 or more, thereby reducing jitter value during overwriting, and at the same time of cross-erase Occurrence can be suppressed.

FIG. 7 illustrates a phase change optical disc according to a second embodiment of the present invention. The phase change optical disc 200 according to the embodiment includes an interference layer 220 and a second layer on a transparent substrate 210 as shown. The first dielectric layer 230, the second dielectric layer 240, the recording layer 250, the third dielectric layer 260, and the reflective layer 270 are sequentially stacked.

Each layer from the substrate 210 to the reflective layer 270 is made of the same material as that of the corresponding layer of the phase change optical disk 100 according to the first embodiment of the present invention shown in FIG. 5. The specific description thereof is omitted.

FIG. 8 illustrates that the interference layer 220 of the phase change optical disk 200 according to the second embodiment of the present invention shown in FIG. 7 is made of aluminum (Al) having a thickness of 6 nm, and the first dielectric layer 230 is Al ₂ O ₃ , the second dielectric layer 240 and the third dielectric layer 260 form ZnS-SiO ₂ with a thickness of 55 nm and 20 nm, respectively, and the recording layer 250 forms Ge ₂ Sb ₂ Te ₅ with 20 nm. In the case where the thickness of the reflective layer 270 is made of aluminum (Al) in a thickness of 100 nm, the reflectance (Rc) and the amorphousness of the recording layer 250 in the crystalline state of the recording layer 250 are varied while changing the thickness of the first dielectric layer 230. The results of calculating the light reflectance (Ra) and the light absorption ratio (Ac / Aa) at are shown in a graph.

Here, referring to FIG. 8, according to the thickness of the first dielectric layer 230 formed of Al ₂ O ₃ having a refractive index of approximately 1.3, the reflectance Rc in the crystalline state of the recording layer 250 and the light reflectivity Ra in the amorphous state And the light absorption ratio (Ac / Aa) is greatly changed, and in particular, the light absorption ratio (Ac / Aa) of the crystalline and amorphous phases of the recording layer 250 in the range of 92 nm to 96 nm is 1.3 or more.

Therefore, when the phase change optical disk using the blue wavelength light as the light source is formed of the layer structure and the material as shown in FIG. 7, the jitter value can be reduced during overwriting and cross-erase. Can be suppressed.

FIG. 9 shows a typical recording laser pulse pattern of a phase change optical disk, which is shown in FIG. 10 to compare, according to the multilayer film structure, the extent to which marks already recorded on adjacent tracks are erased when recording with such pattern pulses. FIG. 11 shows a result of calculating the temperature distribution according to the moving distance from the track center in the y direction in the track structure of the phase change optical disk.

The phase change optical discs shown in FIG. 11 are compared with those of the phase change optical disc 200 of the present invention shown in FIG. 7, the conventional phase change optical disc 10 shown in FIG. 1, and the conventional general four-layer structure (ZnS-SiO _2). A phase change optical disk (not shown) having a dielectric layer, a Ge ₂ Sb ₂ Te ₅ recording layer, a ZnS-SiO ₂ dielectric layer, and an Al reflective layer.

The temperature distribution shown in Fig. 11 determines the recording laser pulse values so that amorphous marks of the same size are formed in the recording layer in the crystalline state with respect to the multilayer film structure of each of the phase change optical disks, and light absorption of the amorphous marks present in adjacent tracks is made. In order to compare the degree of erasing according to the above, it is assumed that the recording layer is in an amorphous state in the multilayer film structure of each phase change optical disk, and the laser pulses obtained above are incident to the multilayer film while being perpendicular to the traveling direction of the laser beam (see FIG. This is the result of calculating the temperature distribution in the y direction).

Referring to the temperature distribution shown in FIG. 11, a phase change optical disk (not shown) of a conventional general four-layer structure, the conventional phase change optical disk 10 shown in FIG. 1, and the phase change optical disk 200 of the present invention shown in FIG. It can be seen that the temperature distribution decreases in the order of). This result is because the optical absorption ratio (Ac / Aa) in the crystalline and amorphous phase of the recording layer is increased to 0.83, 1.0, and 1.3, respectively, in the multilayer structure of each phase change optical disk, so that the amount of light absorption in the amorphous phase is different. This is because the optical absorption ratio (Ac / Aa) in the crystalline and amorphous phase of the recording layer is increased in the multilayer film structure of the phase change optical disk 200 according to the present invention shown in FIG. 7 so that the cross-erase phenomenon is considerably increased. It means to be suppressed.

As described above, according to the phase change optical disk according to the present invention, the optical absorption ratio (Ac / Aa) of the crystalline and amorphous phases of the recording layer is increased, so that even when the blue wavelength light is used as the light source, At the same time, it is possible to reduce the time jitter value and to suppress the occurrence of cross-erase.

Claims (12)

The first dielectric layer, the interference layer, the second dielectric layer, the recording layer, the third dielectric layer, and the reflective layer are sequentially stacked on the substrate, The interference layer is a phase change optical disk, characterized in that made of any one material selected from the group consisting of Al, Ag, GaP and alloys containing them. The first dielectric layer, the interference layer, the second dielectric layer, the recording layer, the third dielectric layer, and the reflective layer are sequentially stacked on the substrate, And the recording layer has a light absorption ratio (Ac / Aa) of 1.0 or more in crystalline and amorphous states. The method according to claim 1 or 2, The first dielectric layer is made of any one material selected from Al ₂ O ₃ , ZnS-SiO ₂ , Si ₃ N ₄ , SiO ₂ , MgF ₂ , NaF ₂ , LiF ₂ , CaF ₂ , and AlF ₂ . Phase change optical disc. The method according to claim 1 or 2, The interference layer is a phase change optical disk, characterized in that formed to have a thickness of less than 20nm. delete The method according to claim 1 or 2, And the recording layer has a phase difference of 5 ° or less in a crystalline and amorphous state. The interference layer, the first dielectric layer, the second dielectric layer, the recording layer, the third dielectric layer, and the reflective layer are sequentially stacked on the substrate, The interference layer is a phase change optical disk, characterized in that made of any one material selected from the group consisting of Al, Ag, GaP and alloys containing them. The interference layer, the first dielectric layer, the second dielectric layer, the recording layer, the third dielectric layer, and the reflective layer are sequentially stacked on the substrate, And the recording layer has a light absorption ratio of 1.0 or more in crystalline and amorphous states. The method according to claim 7 or 8, The first dielectric layer is made of any one material selected from Al ₂ O ₃ , ZnS-SiO ₂ , Si ₃ N ₄ , SiO ₂ , MgF ₂ , NaF ₂ , LiF ₂ , CaF ₂ and AlF ₂ Change optical disc. The method according to claim 7 or 8, The interference layer is a phase change optical disk, characterized in that formed to have a thickness of less than 20nm. delete The method according to claim 7 or 8, And the recording layer has a phase difference of 5 ° or less in a crystalline and amorphous state.

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